Despite the California listing, the Natural Resources Defense Council does not expect that this will cause BPA to appear on warning labels.

California today announced its intent to declare bisphenol A a reproductive hazard.

Under a state law known as Prop. 65, warning signs would be required for consumer items that contain a certain high level of BPA. The chemical is used to make polycarbonate plastic, and also is found in liners of food and beverage cans and some thermal receipts.

Scientists say BPA is an estrogen-like substance that can alter reproductive hormones. California's Office of Environmental Health Hazard Assessment said it based its decision to list BPA as a Prop. 65 chemical on a 2008 report by the National Toxicology Program.

"Bisphenol A meets the criteria for listing as known to the State to cause reproductive toxicity (developmental endpoint) under Proposition 65, based on findings of NTP [the National Toxicology Program]," according to the state agency.

"OEHHA is relying on the NTP’s conclusion in the report that there is clear evidence of adverse developmental effects in laboratory animals at 'high' levels of exposure," according to the state's decision.

The decision was based on laboratory tests by scientists that have shown effects on the body weight, litter size and sexual development of pups when pregnant rats and mice are exposed to high levels of BPA.

The state agency is proposing to set an acceptable level of exposure that is considered fairly high, 290 micrograms per day. As a result, Sarah Janssen of the Natural Resources Defense Council wrote on her blog that the decision “is not likely to trigger any warning labels on canned food or beverages.” The same is probably true for receipts and most other consumer products.

"However," she added, "a listing alone is quite significant and makes official what parents have known for years – BPA is harmful and should be avoided."

Plastics and chemical manufacturers say the compound, which has been used in polycarbonate plastic for 50 years, is safe at levels people are exposed to.

Some testing in recent years has found estrogenic effects in animals at low doses that people are regularly exposed to from consumer products. Those low-dose tests, however, were not considered acceptable to the National Toxicology Program in its 2008 report. The federal agency is now reconsidering that. If they are accepted, then California would likely lower its acceptable dose, which would probably trigger warning signs.

The intent of the law, passed by voters in 1986, is to require manufacturers to warn consumers whenever a chemical is used that has been linked to cancer or reproductive effects. In some cases, companies decide to avoid using the compound rather than put up warning signs in stores or other public places.

BPA is found in most canned foods liners, but it already has been banned from baby bottles, and removed from most hard-shell water bottles. It also has been replaced with another chemical in most thermal receipts, although that chemical, known as BPS, also has been linked to estrogen-like effects.

The state agency will accept public comments for one month before making a final decision listing BPA.